Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$83.79	7.798%	$90.3239	$90.32	$90.30	$90.30
Purchase #2	$89.67	12.414%	$100.8016	$100.80	$100.80	$100.80
Purchase #3	$20.47	9.670%	$22.4494	$22.45	$22.45	$22.40
Purchase #4	$154.77	3.264%	$159.8217	$159.82	$159.80	$159.80
Purchase #5	$238.99	13.440%	$271.1103	$271.11	$271.10	$271.10
Purchase #6	$162.42	5.855%	$171.9297	$171.93	$171.95	$171.90
Purchase #7	$14.40	7.114%	$15.4244	$15.42	$15.40	$15.40
7 purchase totals =	$764.51		$831.8610	$831.85	$831.80	$831.70